# `ADK.Application`
[🔗](https://github.com/zeroasterisk/adk-elixir/blob/main/lib/adk/application.ex#L1)

OTP Application for ADK.

## Supervision Tree

    ADK.Supervisor (rest_for_one)
    ├── ADK.SessionRegistry        — Registry for session lookup by {app, user, session_id}
    ├── ADK.Plugin.Registry        — Agent storing global plugins
    ├── ADK.Auth.InMemoryStore     — Agent for credential storage (dev/test)
    ├── ADK.Artifact.InMemory      — Agent for artifact storage (dev/test)
    ├── ADK.Memory.InMemory        — ETS-backed memory store (dev/test)
    ├── ADK.Session.Store.InMemory — ETS-backed session persistence
    ├── ADK.SessionSupervisor      — DynamicSupervisor for session GenServers
    ├── ADK.RunnerSupervisor       — Task.Supervisor for async agent executions
    ├── ADK.Telemetry.SpanStore    — ETS-backed debug span storage
    ├── ADK.Workflow.Checkpoint.EtsStore — ETS-backed workflow checkpoints
    ├── ADK.Tool.Approval          — GenServer for HITL tool approval (optional)
    ├── ADK.LLM.CircuitBreaker     — Circuit breaker for LLM calls
    └── ADK.LLM.Router             — Smart multi-backend LLM router with failover

Uses `rest_for_one` because sessions depend on the Registry being alive.
If the Registry restarts, all sessions must restart to re-register.

## Configuration

Optional application env to control which children start:

    config :adk,
      start_credential_store: true,   # default true
      start_artifact_store: true,     # default true
      start_circuit_breaker: true,    # default true
      start_llm_router: true,         # default true
      start_approval_server: false,   # default false — enable for HITL in server mode
      circuit_breaker: [              # CircuitBreaker options
        failure_threshold: 5,
        reset_timeout_ms: 60_000
      ],
      llm_router: [                   # LLM Router options
        backends: [],
        fallback_error: :all_backends_failed
      ]

---

*Consult [api-reference.md](api-reference.md) for complete listing*